ABSTRACT
Column tests were performed to study water quality changes in the unsaturated zone as a part of a project concerning the future water supply of Stockholm by artificial recharge. Time-domain reflectometry (TDR) probes, water and gas sampling devices, and devices for microbiological studies were installed in the columns. The hydraulic loads were 1 m3/m2/d in three of the columns and 2 m3/m2/d in the fourth. Free water surfaces appeared after 14–22 weeks in three of the columns. Unsaturated conditions prevailed below the sand surface in all 4 columns. According to a chloride tracer test the mean residence times were 16–18 hours in the columns with a hydraulic load of 1 m3/m2/d, and 10 hours in the column with 2 m3/m2/d. A test with Salmonella bacteriophages gave 2–5 hours shorter first arrival times than the chloride test while the arrival times of the peak concentrations were just 1–2 hours shorter.
